The majority of U.S. Coal preparation industries employ mechanical dewatering techniques such as filtration and centrifugation to reduce the moisture content of fine coal (28 mesh top size) and refuse from processes such as water-only cycloning and froth flotation. Mechanical dewatering is the most economical way of separating water from coal. However, it becomes ineffective for ultra fine coal dewatering because of the larger surface area of the particles. Currently, advanced physical coal cleaning processes are being studied for the benefication of ultra fine coal in order to take advantage of the increased liberation of mineral matter and pyrite that results from ultra fine grinding. Wet processes of ultra fine coal cleaning produce an ultra fine clean coal slurry that is extremely difficult to dewater adequately and presents a variety of handling and transportation problems. Some of the more prevalent problems include increased cost of shipping unwanted moisture, freezing of coal, reduction of BTU content and dust dissemination of the dry ultra fine coal.
Thermal drying is the most effective method for moisture reduction of fine coal and can produce a dry product of even ultra fine coal. However, the process is cost prohibitive. Also, thermal dewatered product owing to its dusty nature and increased reaction rate with oxygen possesses its own set of handling, transportation, and storage problems. Some of these problems include spontaneous combustion, explosion, wind erosion, and dust pollution. Similar problems may arise in the processing of materials such as sulfur, phosphates, clays or other finely divided ores and minerals which may be treated with water and are thereafter dewatered and dried.
The use of binders to agglomerate fine coal prior to thermal drying is known. For example U.S. Pat. No. 4,830,637, Wasson discloses a method and apparatus for increasing the size distribution of a coal preparation plant product by agglomerating dewatered coal fines and cyclone recycled fines prior to thermal drying. The method includes adding a binder to recycle fines from a thermal dryer cyclone underflow to dewatered fines and mixing to form an agglomerate of greater than 28 mesh.
Methods of suppressing coal dust are also known. U.S. Pat. No. 4,561,905, Kittle discloses the use of foamed oil/water emulsions to control coal dust. U.S. Pat. No. 4,780,233, Roe discloses a method of dust suppression for coal and other materials wherein minor amounts of a water insoluble elastomeric polymer are combined with oil containing dust control treatments.